This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-210405, filed Jul. 11, 2000, the entire contents of which are incorporated herein by reference.
This invention relates to a method of detecting malfunctions during the ejecting step of removing molded products from a mold in a motorized or hydraulic injection molding machine.
Injection molding machines are generally operated as follows. First of all, the mold thereof is clamped, and then, a melted material is injected from the injection unit into a mold. Then, after the resin is sufficiently freezed, the releasing of mold is performed. After the releasing of mold, an ejector pin incorporated inside a movable die is allowed to protrude from the inner wall of the die so as to push the molded product out of the die. With respect to this ejecting step, it has been conventionally practiced such that the ejecting speed, ejecting force and stroke of the ejector pin, etc. are set in advance by the operator. However, with regard to the evaluation of the result of product removal from the mold, the measures that have been taken according to the prior art were simply to confirm the ejecting stroke of ejector pin, thus omitting any other automatic evaluation of the result of removal of the molded product.
As mentioned above, according to the control system of the conventional injection molding machine, if only the advancing movement of the ejector pin up to a preset stroke can be confirmed in the ejecting step, the ejecting step is judged as being normally finished, thus enabling the injection molding machine to start the next mold clamping step.
However, there is occasionally a case where the ejector pin is pierced into a molded product, thereby leaving the molded product adhered to and unremoved from the surface of the mold. In such a case, it is impossible according to the conventional control system to recognize the existence of the molded product on the front surface of mold. Therefore, if the next mold clamping operation is performed under such an abnormal condition, the molded product is caught between the pair of dies, thus leading to damage of the mold.
With a view to prevent such an accident, there has been proposed a malfunction-detecting system which is based on image processing. This system however is accompanied with drawbacks that the installation cost thereof is high, and that a delicate adjustment of illumination, etc. is required for obtaining a clear image, thereby making it troublesome in handling the system.
This invention has been accomplished in view of overcoming the problems accompanied with the conventional malfunction-detecting method in the ejecting step of the conventional injection molding machine. Therefore, an object of this invention is to provide a malfunction-detecting method which makes it possible to reliably detect malfunctions in the ejecting step without rendering the injection molding machine more complicated.
Namely, this invention provides a malfunction-detecting method in electric injection molding machines, in which a molded product is removed from a mold by using an ejector pin in an ejecting step, the method comprising the steps of:
storing in advance a relationship between time and torque of an ejector pin driving motor as a reference pattern, the relationship having been obtained from good results in the removal of the molded product;
presetting a tolerance limit of the reference pattern with respect to the value of the torque; and
monitoring a pattern of the torque, relative to time, during the ejecting step, and generating an alarm at the time when the value of the torque falls outside the tolerance limit.
The malfunction-detecting method of this invention to detect a malfunction in an injection molding machine is based on the following principle. Namely, when, for instance, the ejector pin is pierced into a molded product, thus leaving the molded product adhered to and unremoved from the surface of the mold in the ejecting step after the releasing of the mold, the torque of the ejector pin-driving motor is of an abnormal value. Therefore, when a pattern indicating this abnormal value of torque is compared with the normal torque pattern, the occurrence of a malfunction in the ejecting step can be easily detected.
Further, even when the cavity of the mold is under-filled or over-filled, part of a molded product may be adhered to and unremoved from the surface of the mold. Even in this case, the torque of the ejector pin driving motor is of an abnormal value, so that the occurrence of a malfunction in the ejecting step can be reliably detected.
Preferably, a time interval for monitoring the torque pattern of the ejector pin driving motor relative to the time in the ejecting step is possible to be preset by the operator.
By doing so, it becomes possible for the operator to optionally preset in advance, as a monitoring interval, a region where the changes of torque are relatively mild in the torque pattern in the normal operation of the ejecting step, or a region where a pattern peculiar to the generation of various kinds of malfunction is likely to be manifested. As a result, the accuracy in detection of a malfunction can be improved.
Incidentally, the aforementioned malfunction-detecting method can also be applied to a hydraulic injection molding machine in the same manner as that of the electric injection molding machine. In this case however, the pattern to be monitored would be a pattern of the hydraulic pressure of the ejector pin-driving hydraulic pump instead of the pattern of torque of the ejector pin-driving motor.
Incidentally, the aforementioned xe2x80x9ctimexe2x80x9d refers to the time elapsed from the start of the ejecting operation. Instead of using this xe2x80x9ctimexe2x80x9d, either the position of the ejector pin, or the rotation angle of motor for driving the ejector pin can be also utilized.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.